The process of measuring blood flow within a body of a subject non-invasively is useful in diagnosing and treating the subject. This is particularly the case where a part of a subject or patient, such as a tissue or organ, suffers from diseases due, for example, to cancer or malfunction. Determining perfusion indices including the blood flow through such a tissue or organ can provide important information to a physician in order to determine an appropriate treatment regime for the patient.
Existing systems pertaining to blood flow information have been disclosed. In general, the systems involve a contrast agent which is delivered as an intravascular bolus during a dynamic imaging session such as computerised tomography (CT), nuclear medicine (NM) or magnetic resonance imaging (MRI). The temporal profile of the image intensity in a pixel or region of interest (ROI) reflects the characteristics of the contrast agent and hence the blood passing through the tissue.
A typical method of obtaining quantitative perfusion indices involves several steps including:
(a) converting the signal intensity profile to the contrast concentration profile depending on the type of imaging modality;
(b) measuring the arterial input function (AIF) from a feeding vessel to the tissue of interest;
(c) measuring the tissue profile;
(d) extracting the tissue impulse residue function (IRF) from the AIF and tissue profile using deconvolution; and
(e) calculating quantitative perfusion indices including blood flow, blood volume and mean transit time using the IRF.
However, problems arise when obtaining the above-mentioned perfusion indices when the region of interest includes a tissue or organ that moves over time. Cardiac and respiratory motions are two of the most common sources causing motion artefacts during a dynamic imaging scan. For example when a subject is breathing, the lungs and kidneys and other organs and tissues move involuntarily and create motion artefacts. These motion artefacts make it difficult to obtain data in the region of interest between successive time points at a fixed location within the region of interest due to the movement of the tissue or organ in the region of interest. Taking the example of breathing, a lung could move left or right in the coronal plane, up or down in the coronal plane or even in and out of the coronal plane, for example in the sagittal plane. Due to local tissue stretching and non-uniform distortion, these motion artefacts are not easily correctable using conventional image registration methods for the brain. Breath holding, for up to 20 seconds, is the common method during scanning to minimize respiratory motion artefact, however it is not effective for a typical dynamic scan which takes more than 40 seconds. Other methods of minimizing these motion artefacts are by cardiac and/or respiratory gating during a scan subject to limitations of the hardware used.
The present invention seeks a post-processing method to substantially overcome or at least ameliorate, any one or more of the above-mentioned disadvantages associated with motion artefacts in a region of interest of a subject.